The Hunt For Alien Life Through Infrared (IR) Spectroscopy V3
A barcode is all humans need to be able to detect life on different planets. You may be asking what type of barcode could tell you that? Well, utilizing a technique called spectroscopy, analyzing what seems like a barcode would allow humans to do that. “How is that possible?” you might be asking. To see the history of how spectroscopy was developed, we would have to go back to the nineteenth century.
Origins of Spectroscopy & Its Breakthrough
In 1814, German Physicist Joseph von Fraunhofer was trying to solve the problem of chromatic aberration, the reason that telescope images looked blurry and had halos on bright objects. He utilized a glass prism to bend the incoming sunlight into a rainbow spectrum, which revealed the sun spectrum. He had originally observed and discovered the dark absorption lines of the solar spectrum, and only used them as reference marks to measure glass. In 1859, Physicist Gustav Kirchhoff and Chemist Robert Bunsen entered the story of spectroscopy, and made a massive breakthrough for spectroscopy. After Fraunhofer had passed away, everyone was wondering what caused the spectral lines on the Sun. To answer the question, Robert Bunsen used the Bunsen Burner he created in 1855, as the flame was colorless and wouldn’t interfere with the chemicals’ own light that it emitted. They observed the light from the chemicals through a glass prism, and saw that the chemicals left spectral lines. After testing different chemicals, they figured out each chemical has its own fingerprint, a way of identifying it. They concluded that each element/chemical emitted the same light they absorbed.
Spectroscopy Discoveries and Advantages/Disadvantages
The Spectroscope enabled scientist to make so many discoveries, some being: The discovery of Helium, discovering the chemical composition of the Sun and Stars, the discovery of alkali metals rubidium and cesium, the revelation that the universe is expanding through redshift of galaxies, the limitations that the Earth’s atmosphere has on readings, and most importantly the atmospheres of exoplanets and what the chemical composition of some exoplanets are. Cosmic dust is all over the universe and since exoplanets are so far away, their light is more faint and the readings of the cosmic dust heavily overlap the readings of the exoplanet.
Of course with so many benefits, there are always disadvantages. Sometimes when looking through a spectroscope, because of all the cosmic dust it messes up with the readings you get and some of the chemicals overlap. Water can also affect what you see, as it blinds some of the readings and spectral lines and makes it harder to find less apparent chemicals.
Practices of Infrared Spectroscopy
When a planet passes by its star, the molecules from the exoplanet atmosphere absorb some of the infrared light from its own star, or the closest light source. From there, we can use our infrared spectroscope to see what chemicals are present in the planet, such as oxygen, water, and methane. The hint scientists use is that methane and oxygen are present in the exoplanet since oxygen and methane naturally destroy each other. If something is there to produce both chemicals, then a strong hint of life is present on that planet, or at least that’s something we can assume.
One difficult challenge with this is how do scientists know or tell the difference between naturally occurring gases vs gases being produced by living organisms. To explain it, you can’t rely only on Infrared Spectroscopy, but you have to look at and analyze the entire planet. I used methane as an example of a gas that signals life on a planet, but both living organisms and volcanoes produce methane, so how do we tell them apart? Volcanoes throw out massive amounts of carbon monoxide along with carbon dioxide, while living organisms consume carbon monoxide. If we were analyzing a planet that’s rich in methane with minimal carbon monoxide, that is an amazing sign for life on that planet. As stated before oxygen and methane are good signs of life, but there is a possibility that both exist at the same time as a false positive. I’ll be using oxygen, as I have already discussed how the geology of a planet can cause methane production. Oxygen can be supplied by space weather. Highly active stars have harsh ultraviolet light that basically bakes the planet’s atmosphere, ripping water molecules from water into space and leaving the oxygen trapped in the atmosphere. Although both methane and oxygen are great signs of life, they could also be generated by nature. A rich thriving planet could really be a volcanic rock that’s being cooked by its star.
A great example of this is the James Webb Space Telescope (JWST). It can detect infrared glow from exoplanets to see if potential life is present. It also avoids the problem of the Earth’s atmosphere when it tries to read exoplanets chemical composition by orbiting above Earth’s atmosphere. Another example is Airbus Defense and Space. They built the NIRSpec (Near-Infrared Spectrograph) for the European Space Agency with the help of NASA Goddard’s microshutter arrays which observe about 100 objects at a time which are mostly galaxies . The way the NIRSpec was engineered was with 250,000 tiny microscopic doors called the microshutter array that open and close to focus on specific stars it wants to target.
The spectroscopes don’t just send out beautiful photos of the spectral lines. Scientists receive a massive amount of raw data which they have to write code that’s normally Python, specifically algorithms to process data and filter out cosmic dust. They also graph the behavior of light, mapping the sudden drops in intensity that visually represent these spectral lines.
Infrared Spectroscopy on the JWST
In 2023, a research paper titled “Carbon-bearing Molecules in a Possible Hycean Atmosphere,” included information about historic discoveries made by using the James Webb Space Telescope. The planet they were studying was K2–18b, which is an exoplanet about 124 light-years away from Earth that orbits a low-mass red dwarf star known as K2–18. The big discovery was detecting methane and carbon dioxide in high abundance, a scarcity of ammonia, and possible hints of dimethyl sulfide (DMS) which is a molecule that on Earth is produced almost entirely by life, but has been detected on a comet before.
Compared to Earth, it’s about 2.6 times the radius and 8.6 times the mass of Earth. The research paper gathered information that K2–18b is likely to contain a hydrogen rich atmosphere with a planet wide liquid water ocean, being labeled a candidate Hycean planet.
Without Infrared Spectroscopy, specifically Near-Infrared Spectroscopy, this wouldn’t have been possible, as it essentially acts like a fingerprint scanner. When K2–18b passed in front of its host star, different gasses absorbed light at specific wavelengths which revealed dips in light at the wavelengths associated with methane and carbon dioxide which suggest evidence of their existence on that planet. Although not confirmed, the presence of DMS is highly debated. Further investigations are needed to confirm whether the ocean is really liquid water or if it was just the atmospheric pressure that turned the water into a scorching fluid layer.
This investigation continued in 2025 with the research paper titled “New Constraints on DMS and DMDS of K2–18b from JWST MIRI”, which builds on the 2023 findings with the goal of learning more about whether or not life exists on K2–18b. This time, the team utilized JWST’s Mid Infrared Instrument which has the ability to observe longer wavelengths of light than the Near Infrared Instrument used in 2023. Dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) have absorption features in the range of the instrument, so this would give scientists a new way to look for them.
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The researchers reported unconfirmed evidence of DMS and DMDS at a statistical significance of around 3 sigma. This is an interesting hint but not quite a discovery since confirmed detections are around 5 sigma. This suggests that DMS and DMDS could be in high concentrations, about 10 parts per million. The signals still remain debated, with other research groups analyzing the same JWST data and finding no evidence for DMS or DMDS and arguing that the signals come from other molecules or something like noise messing up the data. The new data gathered also made room for models for a planet with a magma ocean or a gas-rich mini Neptune. It’s still a very promising target to continue researching, but scientists still need strong evidence of life. This research highlights how infrared spectroscopy can search for molecular signatures of life, but how there is still uncertainty in the research and that the research needs to be carefully analyzed.
My Hot Take on IR Spectroscopy
Although this concept is super cool, I do have a hot take for this. We as humans, specifically scientists and the media, are too eager to announce extraterrestrial life. An example of this could be K2–18b. There’s constant back and forth claims of signals of life present on the planet, there’s a debate on which planet model K2–18b fits, and the detection fell short of the 5 sigma expectation. Headlines were ahead of the actual evidence. Infrared spectroscopy can’t settle the debate between life or just nature since it can’t detect if something was caused by a living organism.
I would argue it’s better to look for signals of life that aren’t like us. We can’t rely on DMS or DMDS to give us hints on if life exists on another planet only because it’s generated by Earth’s life. One idea could be Silicon based life. Extraterrestrial life that bonds with silicon rather than carbon like humans. The only limitation with this is that silicon chemistry isn’t versatile or practical for investigating or utilizing instruments like the JWST.
If scientists wanted to look for more technologically developed life, they could make an algorithm that looks for artificial chemicals such as chlorofluorocarbons (CFC’s) which would strongly support the claim of the existence of alien industries. Chlorofluorocarbons are technosignatures, which are similar to biosignatures except it’s harder and rarer for them to be naturally produced. If an infrared spectroscope detected high levels of CFCs, then there is a good chance there is an alien civilization on the planet. For scientists to find them, they would have to build algorithms that detect their spectral fingerprint. The code (algorithms) could potentially map out the chemical footprint of an active extraterrestrial civilization if found.
Conclusion:
Spectroscopy can give us the barcode, but reading it is the real challenge. I hope you enjoyed it!
About The Author:
My name is Marco Alejandre Ponce, a 10th grader in California who is interested in Astronomy, Astrophysics, Coding, and Electrical Engineering. I’m someone who loves a good challenge and strives to make things more difficult for me since it can teach me more if I take an easy route.
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